The invention relates to a system for supplying liquefied gas as fuel to a combustion engine, comprising a line for supplying gas to the engine, a liquefied gas source, a minimum liquefied-gas level detector and a means for indicating detection of the minimum level.
Many industrial vehicles use liquefied petroleum gas as fuel. The fuel is stored on the vehicle either in a changeable bottle or in a fixed tank. In the first case, the driver changes the bottle when the fuel is about to run out, while in the second case the driver must drive to a filling station in order to fill the tank.
These two storage modes each have a major drawback:
When the fuel is stored in a bottle, the driver has no information about the fuel level remaining in the bottle. To avoid running out of fuel, the driver has no other alternative but to regularly change the bottle, which generates substantial waste.
When the fuel is stored in a tank, the tank must be filled in a filling station. The filling is carried out on the basis of the differential pressure principle: the pressure of the gas contained in the station's tank “pushes” the liquid phase of the fuel into the vehicle's tank where the pressure is lower. If the pressure of the gas remaining in the tank is above the pressure of the gas in the filling station, filling is impossible. This may occur when the vehicle is running in a high temperature environment (for example a tank exposed to sunshine).
To remedy this problem there exists in the prior art an end-of-fuel-supply detection system that detects the drop in gas pressure. This system is placed in the fuel supply line downstream of the fuel source and upstream of the pressure regulator. When the fuel is about to run out, the pressure of the fuel source drops and a pressure-activated switch turns on a warning light on the dashboard. This system is not reliable as the pressure is directly proportional to temperature—therefore the time remaining before running out of fuel is random and may vary from a few minutes to a few seconds. In most cases, the warning light is turned on at the moment when the engine stalls for lack of sufficient fuel. Since the system is not reliable, the driver ignores the information displayed on the dashboard.
Other manufacturers place a second bottle on the vehicle. This method is not very practical since the vehicle's engine stops when the bottle is empty. If this occurs during a maneuver with a heavy load, the vehicle stops suddenly, and this may be hazardous. In addition, it turns out that some drivers do not automatically replace the empty bottle, the breakdown then occurring when the second bottle is empty.